You should do it! Showing is a great experience, as I'm sure you know. Make sure you've schooled anything they can ask for in the classes you're signed up for. I did a class once that included a hand-gallop, extended trot with no stirrups, figure-eight with a flying change, etc. It was clear who hadn't done their homework. So check the tests that can be asked of your class and practice, practice, practice them at home, especially for the medals.
I'm not sure how much you've looked into big eq horses, but be prepared for the price. For an good horse with extensive 3'6" show-ring experience that can do Medal/Maclay and Talent Search prices are generally pretty pricy. When I was down in Florida, there was a nice hunter with potential going for $80k. I've seen a lot of very nice 4' hunters going for well into the six figures. I'm not saying less expensive horses aren't out there, you just have to look in the right places.
I'd definitely go for it, have fun! :)